All of these sacks were obtained pre 5.1. They were opened today, at 5.1. They contained evolution stones that only exist in 5.1. Therefore, stuff is generated on opening.

(Although, based on the weighting of things I got, and the fact that I usually fight the same Pandaren - that Dragon one came from Aki, most likely - they might keep track of exactly which gym leader the sack came from. Just an observation. Not saying it's true, just very possible.)

Updated info: They have recently changed these bags to reward indolence and punish hard work. They track how many battlestones you have gotten and ADJUST YOUR LOOT. If you farm these heavily, you will soon be opening twelve per day and getting no stones at all. Farming these on alts instead would be a good counter to this.

Comment by Aquifel

Found this info on the official WoW Forums, all credit for the data go to Avengener@Barthilas:

Comment by mezmorized

^ UPVOTE ME :).... THX

Here is a tip if your looking for an easy way to grind these trainers.

Create 11 toons on a empty server. I would choose RP server (So you don't get ganked). Luckily, I have several accounts and the RP server is in my CRZ. I got my level 90 mage and ported 7 of them to Eternal Vale, 1 to Dalaran. I flew them out to the each of the Grand Master Pet Trainers.

Comment by snyps

Comment by Aglaia

I hate the new way to open the bags. Why it cannot be a normal bag anymore? I have no chance to take only the items i need out and delete the bag afterwards.No I have to be always scared that i do not have enough free bag slots.

Comment by Novalix

It seems they dramatically increased the drop rate of flawless family specific battle stones when they changed how the bags open.

This change was done to prevent an abuse of opening the bags.

Comment by swiftarroww

I have a question, on the Pandaren Spirit Tamers, Can you do them daily to get chances for their pets?

Comment by ADDbutterfly

Just a few minutes ago I got the Flawless Undead Battle-Stone from Lydia Accoste in Karazhan. I used Darkmoon Glowfly and Cogblade Raptor both level 25. I also had a Kun Lai Runt but he died. He was level 23.

Comment by depaR

It confused me for a while too, so I thought it might be worth a post:

To open, double right click on it! I couldn't figure it out for a while. :)

Comment by geekygirlish

I wonder if they have nerfed this loot wrt battle stones. I do my round of trainers almost every day and in the past I could count on getting at least one battlestone of some variety. I haven't seen one in weeks, just the useless vendor trash and bandages

Comment by mickwald

I put together a few scripts that tell you which daily quests you haven't finished yet. These include all the grandmasters, Pandaren tamers as well as the Pandaren Spirit tamers. So basically all trainers with a daily quest that grants some kinde of bag.

/run if (not IsQuestFlaggedCompleted(31958)) then print("Aki") end/run if (not IsQuestFlaggedCompleted(31955)) then print("Nishi") end/run if (not IsQuestFlaggedCompleted(31991)) then print("Zusshi") end/run if (not IsQuestFlaggedCompleted(31953)) then print("Hyuna") end/run if (not IsQuestFlaggedCompleted(31954)) then print("Moruk") end/run if (not IsQuestFlaggedCompleted(31956)) then print("Yon") end/run if (not IsQuestFlaggedCompleted(31957)) then print("Shu") end/run if (not IsQuestFlaggedCompleted(31971)) then print("Obalis") end/run if (not IsQuestFlaggedCompleted(31935)) then print("Payne") end/run if (not IsQuestFlaggedCompleted(31926)) then print("Antari") end/run if (not IsQuestFlaggedCompleted(31916)) then print("Accoste") end/run if (not IsQuestFlaggedCompleted(31909)) then print("Trixxy") end/run if (not IsQuestFlaggedCompleted(32434)) then print("Burning") end/run if (not IsQuestFlaggedCompleted(32439)) then print("Flowing") end/run if (not IsQuestFlaggedCompleted(32441)) then print("Thundering") end/run if (not IsQuestFlaggedCompleted(32440)) then print("Whispering") end